1. Field of the Invention
The present invention relates to an inter-digital transducer provided with a balanced type terminal, a longitudinally coupled mode type surface acoustic wave filter and a communication apparatus using the same.
2. Description of the Related Art
As the electromechanical function parts using surface acoustic wave (SAW) have been noted with attention in the current of making the hardware high density because the acoustic velocity of wave is several kilometers/second, and the wave energy has properties to be concentrated on the surface of the propagation medium. Due to the development of inter-digital transducer (IDT) electrode and progress of the thin film preparing technique and surface processing technique, the SAW has been practically utilized for delay line for radar, band-pass filter for television receiver, etc. At present, the SAW is extensively used as RF and IF stage filters for receiving and transmitting circuits in radio-communication apparatus.
Conventionally, there are known transversal SAW filter and two kinds of longitudinally coupled mode coupled and transverse mode coupled type SAW filters. The transversal SAW filter has small group delay variation characteristic, but it has large insertion loss and large element size. On the other hand, the mode coupled type SAW filter presents steep attenuation characteristic, shows small insertion loss, and is small in element size, but its group delay variation characteristic is inferior to that of transversal type SAW filter. The longitudinally coupled mode type SAW filter is characterized by having relatively wide pass band, and the transverse mode type SAW filter is characterized by having very narrow pass band characteristic. In view of the above characteristics, as the RF filter for the mobile communication apparatus, the longitudinally coupled mode coupled type filter, and as the IF filter, the transverse mode coupled type SAW filter which is miniature in size and excellent in attenuation characteristic have been widely used.
Furthermore, balancing of semiconductor parts such as IC has advanced in recent years in order to reduce noise characteristics and balancing is also required for surface acoustic wave filters used for the RF stage. Furthermore, from the standpoint of impedance matching with ICs placed before and after, control over impedance of surface acoustic wave is required in recent years.
A surface acoustic wave filter used for the RF stage will be explained first as a first conventional technology.
A longitudinally coupled mode type surface acoustic wave filter having a conventional balanced type input/output terminals will be explained below.
FIG. A12 shows a configuration of a longitudinally coupled mode type surface acoustic wave filter having conventional balanced type input/output terminals. In FIG. A12, the surface acoustic wave filter is constructed by forming input IDT electrodes 3002a and 3002b, reflector electrodes 3003a and 3003b and output IDT electrode 3004 on a piezoelectric substrate 3001. The electrode fingers of the input IDT electrodes 3002a and 3002b on the same side are connected to an input terminal S and the other fingers are grounded. Furthermore, the upper electrode digit of the output IDT electrode 3004 is connected to one output terminal T1 and the lower electrode digit of the output IDT electrode 3004 is connected to the other output terminal T2. By adopting the above-described configuration, a surface acoustic wave filter having balanced type output terminals is obtained.
Then, a surface acoustic wave filter used for the IF stage will be explained as a second conventional technology.
A conventional transversal mode coupled type surface acoustic wave filter will be explained below.
FIG. B24 is a block diagram showing a transversal mode coupled resonator type surface acoustic wave filter according to a conventional technology. In FIG. B24, reference numeral 241 denotes a single crystal piezoelectric substrate and by forming an electrode pattern on this piezoelectric substrate 241, it is possible to excite surface acoustic wave. Reference numeral 242a denotes an IDT electrode formed on the piezoelectric substrate 241 and reflector electrodes 242b and 242c are placed on both sides of the IDT electrode forming thereby an energy-containment type surface acoustic wave resonator. Furthermore, an IDT electrode 243a, reflector electrodes 243b and 243c form a similar surface acoustic wave resonator on the piezoelectric substrate 241. These two resonators are placed close to each other and a surface acoustic wave filter is formed by generating acoustic coupling between these resonators.
In the surface acoustic wave filter configured as shown above, two kinds of surface acoustic wave mode frequencies to be excited on the piezoelectric substrate are determined according to the aperture length of the electrode fingers of the IDT electrodes and the distance between the two surface acoustic wave resonators placed close to each other and the passing bandwidth of the filter is determined.
However, the surface acoustic wave filters explained in the first and second conventional technologies are required to have impedance matching with IC elements in the preceding and following stages, and since the input/output impedance of the above-described conventional filters is dependent on the number of pairs of electrode fingers included in the IDT electrodes and aperture length closely associated with the filter characteristic, there is a problem that it is difficult to attain a desired filter characteristic and a desired impedance value simultaneously.
In view of the above-described problems, the present invention has as its object to provide an inter-digital transducer, a surface acoustic wave filter having an optimal balancing and controlling input/output impedance and communication apparatus using it.
In view of the above-described problems, it is another object of the present invention to provide an inter-digital transducer, a surface acoustic wave filter having desired input/output impedance and communication apparatus using it.
The 1st invention of the present invention is an inter-digital transducer comprising:
a piezoelectric substrate; and
an IDT (inter-digital transducer) electrode having a pair of upper bus bar electrode and lower bus bar electrode placed facing each other on said piezoelectric substrate and a plurality of electrode fingers placed on said piezoelectric substrate each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode,
wherein said IDT electrode is constructed of a plurality of divisional IDT electrodes and connected to a balanced type terminal.
The 2nd invention of the present invention is the inter-digital transducer according to 1st invention, wherein at least two of said plurality of divisional IDT electrodes are equivalently connected in series and at least one of the remaining divisional IDT electrodes is connected in parallel with said at least two divisional IDT electrodes.
The 3rd invention of the present invention is the inter-digital transducer according to 2nd invention, wherein the ratio in the number of electrode fingers among said plurality of divisional IDT electrodes is adjusted beforehand so as to have a predetermined impedance value.
The 4th invention of the present invention is the inter-digital transducer according to 3rd invention, wherein said plurality of divisional IDT electrodes is placed in an same/reverse phase relationship so that charges of the divisional IDT electrodes do not cancel out each other.
The 5th invention of the present invention is the inter-digital transducer according to 4th invention, wherein said plurality of divisional IDT electrodes is constructed of first, second and third divisional IDT electrodes.
The 6th invention of the present invention is the inter-digital transducer according to 5th invention,
wherein said second divisional IDT electrode is placed in same phase relationship between said first divisional IDT electrode and said third divisional IDT electrode,
the part of said upper bus bar electrode corresponding to said first divisional IDT electrode and the part of said upper bus bar electrode corresponding to said second divisional IDT electrode are connected to one end of said balanced type terminal, and the part of said lower bus bar electrode corresponding to said second divisional IDT electrode and the part of said lower bus bar electrode corresponding to said third divisional IDT electrode are connected to the other end of said balanced type terminal.
The 7th invention of the present invention is the inter-digital transducer according to 6th invention, wherein said same phase relationship is a relationship between a pair of said mutually adjacent electrode fingers and that a pair of said mutually adjacent electrode fingers have an same phase relationship means (1) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1/2)xc3x97xcex (here, m=0, 1, 2, 3, . . . , where xcex is a wavelength of an excited surface acoustic wave) and of those electrode fingers, one electrode digit is connected to said upper bus bar electrode and the other electrode digit is connected to the lower bus bar electrode, or (2) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said upper bus bar electrode, or (3) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said lower bus bar electrode.
The 8th invention of the present invention is the inter-digital transducer according to 7th invention, wherein substantially all adjacent pairs of electrode fingers of said plurality of electrode fingers have an same phase relationship and
said substantially all of the plurality of electrode fingers is connected so that charges of the electrode fingers do not cancel out each other.
The 9th invention of the present invention is the inter-digital transducer according to 6th invention, wherein both the part of said lower bus bar electrode corresponding to said first divisional IDT electrode and the part of said upper bus bar electrode corresponding to said third divisional IDT electrode are grounded.
The 10th invention of the present invention is the inter-digital transducer according to 6th invention, wherein the part of said lower bus bar electrode corresponding to said first divisional IDT electrode is connected to the part of said upper bus bar electrode corresponding to said third divisional IDT electrode.
The 11th invention of the present invention is the inter-digital transducer according to 5th invention, wherein said second divisional IDT electrode is placed between said first divisional IDT electrode and said third divisional IDT electrode, the part of said lower bus bar electrode corresponding to said first divisional IDT electrode is connected to the part of said upper bus bar electrode corresponding to said second divisional IDT electrode, and the part of said lower bus bar electrode corresponding to said second divisional IDT electrode is connected to the part of said lower bus bar electrode corresponding to said third divisional IDT electrode.
The 12th invention of the present invention is the inter-digital transducer according to 11th invention, wherein adjacent electrode fingers of said first divisional IDT electrode and said second divisional IDT electrode have an reverse phase relationship, adjacent electrode fingers of said second divisional IDT electrode and said third divisional IDT electrode have an same phase relationship and said substantially all of the plurality of electrode fingers is connected so that respective charges do not cancel out each other.
The 13th invention of the present invention is the inter-digital transducer according to 12th invention,
wherein that said pair of electrode fingers have an same phase relationship refers to a relationship when said pair of electrode fingers are mutually adjacent and (1) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1/2)xc3x97xcex (here, m=0, 1, 2, 3, . . . , where xcex is a wavelength of an excited surface acoustic wave) and of those electrode fingers, one electrode digit is connected to said upper bus bar electrode and the other electrode digit is connected to the lower bus bar electrode, or (2) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said upper bus bar electrode, or (3) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said lower bus bar electrode, and
that said pair of electrode fingers have an reverse phase relationship refers to a relationship when said pair of electrode fingers are mutually adjacent and (4) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1/2)xc3x97xcex (here, m=0, 1, 2, 3, . . . , where xcex is a wavelength of an excited surface acoustic wave) and both electrode fingers are connected to said upper bus bar electrode, or (5) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1/2)xc3x97xcex and both electrode fingers are connected to said lower bus bar electrode, or (6) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and of those electrode fingers, one electrode digit is connected to said upper bus bar electrode and the other electrode digit is connected to the lower bus bar electrode.
The 14th invention of the present invention is the inter-digital transducer according to 11th invention, wherein both the upper bus bar electrode of said first divisional IDT electrode and the lower bus bar electrode of said third divisional IDT electrode are grounded.
The 15th invention of the present invention is the inter-digital transducer according to 11th invention, wherein the upper bus bar electrode of said first divisional IDT electrode is connected to the lower bus bar electrode of said third divisional IDT electrode.
The 16th invention of the present invention is the inter-digital transducer according to 4th invention, wherein said plurality of divisional IDT electrodes is constructed of first, second, third and fourth divisional IDT electrodes.
The 17th invention of the present invention is the inter-digital transducer according to 16th invention,
wherein said plurality of divisional IDT electrodes is placed in order of said first, second, third and fourth divisional IDT electrodes,
the part of said upper bus bar electrode corresponding to said first divisional IDT electrode, the part of said upper bus bar electrode corresponding to said third divisional IDT electrode and the part of said upper bus bar electrode corresponding to said fourth divisional IDT electrode are connected, and
the part of said lower bus bar electrode corresponding to said first divisional IDT electrode, the part of said lower bus bar electrode corresponding to said second divisional IDT electrode and the part of said lower bus bar electrode corresponding to said fourth divisional IDT electrode are connected.
The 18th invention of the present invention is the inter-digital transducer according to 17th invention,
wherein said same phase relationship refers to a relationship between a pair of said mutually adjacent electrode fingers and that said pair of mutually adjacent electrode fingers are in an same phase relationship means (1) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1/2)xc3x97xcex (here, m=0, 1, 2, 3, . . . , where xcex is a wavelength of an excited surface acoustic wave) and of those electrode fingers, one electrode digit is connected to said upper bus bar electrode and the other electrode digit is connected to the lower bus bar electrode, or (2) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said upper bus bar electrode, or (3) a connection relationship in which the pitch between said pair of mutually adjacent electrode fingers is (m+1)xc3x97xcex and both electrode fingers are connected to said lower bus bar electrode.
The 19th invention of the present invention is the inter-digital transducer according to 18th invention,
wherein of said plurality of electrode fingers, substantially all adjacent pairs of electrode fingers are in an same phase relationship and substantially all of the plurality of electrode fingers is connected so that respective charges do not cancel out each other.
The 20th invention of the present invention is the inter-digital transducer according to 17th invention,
wherein the part of said upper bus bar electrode corresponding to said second IDT electrode is grounded and the part of said lower bus bar electrode corresponding to said third IDT electrode is grounded.
The 21st invention of the present invention is the inter-digital transducer according to 17th invention,
wherein the part of said upper bus bar electrode corresponding to said second IDT electrode is connected to the part of said lower bus bar electrode corresponding to said third IDT electrode.
The 22nd invention of the present invention is the inter-digital transducer according to 21st invention,
wherein said xe2x80x9cconnectionxe2x80x9d means that, of adjacent electrode fingers of said second divisional IDT electrode and said third divisional IDT electrode, said second divisional IDT electrode digit is connected to both the part of said upper electrode corresponding to said second divisional IDT electrode and the part of said lower electrode corresponding to said third divisional IDT electrode, and
of adjacent electrode fingers said third divisional IDT electrode digit is connected to both the part of said lower electrode corresponding to said third divisional IDT electrode and the part of said upper electrode corresponding to said second divisional IDT electrode.
The 23rd invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
a plurality of IDT (inter-digital transducer) electrodes having a pair of upper bus bar electrode and lower bus bar electrode facing each other placed on said piezoelectric substrate and a plurality of electrode fingers each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode; and
a plurality of reflector electrodes,
said surface acoustic wave filter being a longitudinally coupled mode type surface acoustic wave filter in which said plurality of IDT electrodes and said plurality of reflector electrodes are placed in the propagation directions of surface acoustic waves respectively,
wherein at least one of said plurality of IDT electrodes is the IDT electrode of the inter-digital transducer according to any one of 1st to 4th inventions and said piezoelectric substrate is the piezoelectric substrate of said inter-digital transducer.
The 24th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
three IDT (inter-digital transducer) electrodes having a pair of upper bus bar electrode and lower bus bar electrode facing each other placed on said piezoelectric substrate and a plurality of electrode fingers each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode; and
at least two reflector electrodes,
said surface acoustic wave filter being a longitudinally coupled mode type surface acoustic wave filter in which said three IDT electrodes and said at least two reflector electrodes are placed in the propagation directions of surface acoustic waves,
wherein at least one of said three IDT electrodes is the IDT electrode of the inter-digital transducer according to 5th invention,
the part of said upper bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said first divisional IDT electrode and/or the part of said upper bus bar electrode of said IDT electrode corresponding to said second divisional IDT electrode are connected to one end of said balanced type terminal of said inter-digital transducer,
the part of said lower bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said second divisional IDT electrode and/or the part of said lower bus bar electrode of said IDT electrode corresponding to said third divisional IDT electrode are connected to the other end of said balanced type terminal of said inter-digital transducer, and
said piezoelectric substrate is the piezoelectric substrate of said inter-digital transducer.
The 25th invention of the present invention is the surface acoustic wave filter according to 24th invention,
wherein said three IDT electrodes are first, second and third IDT electrodes,
said second IDT electrode and said third IDT electrode are placed on both sides of said first IDT electrode respectively,
said reflector electrodes are placed opposite said first IDT electrode of said second IDT electrode and opposite said first IDT electrode of said third IDT electrode respectively, and
said first IDT electrode is the IDT electrode of said inter-digital transducer.
The 26th invention of the present invention is the surface acoustic wave filter according to 25th invention, wherein the upper bus bar electrode of said second IDT electrode is connected to an unbalanced type terminal and the lower bus bar electrode is grounded and the lower bus bar electrode of said third IDT electrode is connected to said unbalanced type terminal and the upper bus bar electrode is grounded.
The 27th invention of the present invention is the surface acoustic wave filter according to 24th invention, wherein a surface acoustic wave resonator is connected in series to and/or in parallel with at least two of said IDT electrodes.
The 28th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
a plurality of longitudinally coupled mode type surface acoustic wave filters having a plurality of IDT electrodes and a plurality of reflector electrodes placed on said piezoelectric substrate,
wherein said plurality of surface acoustic wave filters are connected in multiple stages,
of said plurality of surface acoustic wave filters, at least the surface acoustic wave filters on the input side and/or the surface acoustic wave filters on the output side are the surface acoustic wave filters according to 24th invention, and
said piezoelectric substrates of at least the surface acoustic wave filters on the input side and/or the surface acoustic wave filters on the output side of said plurality of surface acoustic wave filters are the piezoelectric substrates of the surface acoustic wave filters according to 24th invention.
The 29th invention of the present invention is the surface acoustic wave filter according to 28th invention,
wherein said plurality means 2,
said plurality of acoustic wave filters are a first surface acoustic wave filter and a second surface acoustic wave filter,
said first and second surface acoustic wave filters each comprise at least three IDT electrodes,
said first and second surface acoustic wave filters are connected in cascade form,
said first and second surface acoustic wave filters are connected at two points using at least two IDT electrodes, and
the phase of one signal of said IDT electrode is opposite the phase of the other signal of said IDT electrode.
The 30th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
three IDT (inter-digital transducer) electrodes having a pair of upper bus bar electrode and lower bus bar electrode facing each other placed on said piezoelectric substrate and a plurality of electrode fingers each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode; and
at least two reflector electrodes,
said surface acoustic wave filter being a longitudinally coupled mode type surface acoustic wave filter in which said three IDT electrodes and said at least two reflector electrodes are placed in the propagation directions of surface acoustic waves respectively,
wherein at least one of said three IDT electrodes is the IDT electrode of the inter-digital transducer according to 16th invention,
the part of said upper bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said first divisional IDT electrode and/or the part of said upper bus bar electrode of said IDT electrode corresponding to said third divisional IDT electrode and/or the part of said upper bus bar electrode of said IDT electrode corresponding to said fourth divisional IDT electrode are connected to one end of said balanced type terminal of said inter-digital transducer,
the part of said lower bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said first divisional IDT electrode and/or the part of said lower bus bar electrode of said IDT electrode corresponding to said second divisional IDT electrode and the part of said lower bus bar electrode of said IDT electrode corresponding to said fourth divisional IDT electrode are connected to the other end of said balanced type terminal, and
said piezoelectric substrate is the piezoelectric substrate of said inter-digital transducer.
The 31st invention of the present invention is the surface acoustic wave filter according to 30th invention,
wherein said three IDT electrodes are first, second and third IDT electrodes,
said second IDT electrode and said third IDT electrode are placed on both sides of said first IDT electrode respectively,
said reflector electrodes are placed opposite said first IDT electrode of said second IDT electrode and opposite said first IDT electrode of said third IDT electrode respectively, and
said first IDT electrode is the IDT electrode of said inter-digital transducer.
The 32nd invention of the present invention is the surface acoustic wave filter according to 31st invention, wherein the upper bus bar electrode of said second IDT electrode is connected to an unbalanced type terminal and the lower bus bar electrode is grounded and the lower bus bar electrode of said third IDT electrode is connected to said unbalanced type terminal and the upper bus bar electrode is grounded.
The 33rd invention of the present invention is the surface acoustic wave filter according to 30th invention, wherein a surface acoustic wave resonator is connected in series to and/or in parallel with at least two of said IDT electrodes.
The 34th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
a plurality of longitudinally coupled mode type surface acoustic wave filters having a plurality of IDT electrodes and a plurality of reflector electrodes placed on said piezoelectric substrate,
wherein said plurality of surface acoustic wave filters are connected in multiple stages,
of said plurality of surface acoustic wave filters, at least the surface acoustic wave filters on the input side and/or the surface acoustic wave filters on the output side are the surface acoustic wave filters according to 30th invention, and
said piezoelectric substrates of at least the surface acoustic wave filters on the input side and/or the surface acoustic wave filters on the output side of said plurality of surface acoustic wave filters are the piezoelectric substrates of the surface acoustic wave filters according to 30th invention.
The 35th invention of the present invention is the surface acoustic wave filter according to 34th invention,
wherein said plurality means two,
said plurality of acoustic wave filters are a first surface acoustic wave filter and a second surface acoustic wave filter,
said first and second surface acoustic wave filters each comprise at least three IDT electrodes,
said first and second surface acoustic wave filters are connected in cascade form,
said first and second surface acoustic wave filters are connected at two points using at least two IDT electrodes, and
the phase of one signal of said IDT electrode is opposite the phase of the other signal of said IDT electrode.
The 36th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
two IDT (inter-digital transducer) electrodes having a pair of upper bus bar electrode and lower bus bar electrode facing each other placed on said piezoelectric substrate and a plurality of electrode fingers each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode; and
a plurality of reflector electrodes,
said surface acoustic wave filter being a longitudinally coupled mode type surface acoustic wave filter in which said two IDT electrodes and said plurality of reflector electrodes are placed in the propagation directions of surface acoustic waves respectively,
wherein at least one of said two IDT electrodes is the IDT electrode of the inter-digital transducer according to 5th invention,
the part of said upper bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said first divisional IDT electrode and/or the part of said upper bus bar electrode of said IDT electrode corresponding to said second divisional IDT electrode are connected to one end of said balanced type terminal of said inter-digital transducer,
the part of said lower bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said second divisional IDT electrode and/or the part of said lower bus bar electrode of said IDT electrode corresponding to said third divisional IDT electrode are connected to the other end of said balanced type terminal, and
said piezoelectric substrate is the piezoelectric substrate of said inter-digital transducer.
The 37th invention of the present invention is the surface acoustic wave filter according to 36th invention,
wherein said two IDT electrodes are a first and second IDT electrodes,
said second IDT electrode is placed on one end of said first IDT electrode,
said reflector electrodes are placed opposite said second IDT electrode of said first IDT electrode and opposite said first IDT electrode of said second IDT electrode respectively, and
said first IDT electrode is the IDT electrode of said inter-digital transducer.
The 38th invention of the present invention is a surface acoustic wave filter comprising:
a piezoelectric substrate;
five IDT (inter-digital transducer) electrodes having a pair of upper bus bar electrode and lower bus bar electrode facing each other placed on said piezoelectric substrate and a plurality of electrode fingers each being led out from either said upper bus bar electrode or said lower bus bar electrode toward the other bus bar electrode; and
at least two reflector electrodes,
said surface acoustic wave filter being a longitudinally coupled mode type surface acoustic wave filter in which said five IDT electrodes and said plurality of reflector electrodes are placed in the propagation directions of surface acoustic waves respectively,
wherein at least one of said five IDT electrodes is the IDT electrode of the inter-digital transducer according to 5th invention,
the part of said upper bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said first divisional IDT electrode and/or the part of said upper bus bar electrode of said IDT electrode corresponding to said second divisional IDT electrode are connected to one end of a balanced type terminal,
the part of said lower bus bar electrode of said IDT electrode of said inter-digital transducer corresponding to said second divisional IDT electrode and/or the part of said lower bus bar electrode of said IDT electrode corresponding to said third divisional IDT electrode are connected to the other end of said balanced type terminal, and
said piezoelectric substrate is the piezoelectric substrate of said inter-digital transducer.
The 39th invention of the present invention is a communication apparatus comprising:
a transmission circuit that outputs transmission waves; and
a reception circuit that receives reception waves,
wherein the surface acoustic wave filter used for said transmission circuit and/or said reception circuit is the inter-digital transducer according to 1st invention.
The 40th invention of the present invention is a communication apparatus comprising:
a transmission circuit that outputs transmission waves; and
a reception circuit that receives reception waves,
wherein the surface acoustic wave filter used for said transmission circuit and/or said reception circuit is the surface acoustic wave filter according to 23rd invention.